1. Field of the Invention
This invention relates to a method for removing As, or As and Sb and/or Bi from an acidic solution of sulfuric acid so as to separate impurities from acidic solution of sulfuric acid such as a copper electrolyte containing at least arsenic among arsenic, antimony and bismuth as impurities.
2. Description of the Prior Art
In refining a nonferrous metal, particularly in electrolytically refining copper, impurities contained in a crude copper plate such as nickel, arsenic, antimony and bismuth will dissolve out into the electrolyte. When their concentration is above a limit, the quality of the electrolytic copper will be reduced. Therefore, a purification step for removing such impurities from the electrolyte is necessary.
In a conventional purification step for electrolytically refining copper, arsenic, antimony and bismuth have been removed by a copper liberating electrolytic method wherein such components are electrolytically collected as a slime together with copper in the solution by using an insoluble anode. (A. Butts:Copper, The Science and Technology of the Metal, Its Alloys and Compounds, 1954, pp. 204-211)
However, in such a method, as the above mentioned impurities are removed together with copper, copper liberated from the solution will necessarily be contained in the slime and it will be necessary to retreat the slime in the prestep of smelting copper. Thus this method is not satisfactory as a method of discharging the above mentioned impurities out of the system.
If a neutralizing method wherein sodium carbonate or the like is added into the solution is used, the consumption of free sulfuric acid and the contamination of heterogeneous metallic ions (such as Na.sup.++ and Ca.sup.++) into the solution will increase. Thus it is not an appropriate method of purifying the copper electrolyte.
Furthermore, use of an analytic chemical method has been considered wherein hydrogen sulfide is blown into the solution to precipitate arsenic and other impurities as sulfides.
In such a case, copper will coprecipitate and will be contained in the precipitate. Therefore, it is necessary to work such purification method while taking the balance of the copper concentration and sulfuric acid concentration in the electrolyte into consideration.